The present invention relates generally to the field of treating cuttings which are a bi-product of the well drilling process, and, more particularly, to the field of remediation of cuttings from such a process to eliminate the need for toxic waste disposal treatment of cuttings.
The oil and gas well drilling process involves the use of drilling fluid known in the field as drilling mud. Drilling mud formulation technology is very advanced, often including the addition to the water or oil base of heavy additives which are more expensive than the oil that is ultimately produced. For this reason, the recovery and recycling of the expensive drilling fluid is critical to the economic success of the drilling process.
The steps of recovering and recycling drill mud includes the separation of the drilling mud from the cuttings produced in drilling the well. For example, shale shakers have been used for years as a first step in removing the largest cuttings from the drilling mud. In recent years, centrifuge systems having a number of stages have proven to be very effective in removing the drilling fluid from the cuttings, to the point that governmental regulations require that in certain environments the drilling mud, based primarily on a synthetic oil product for off-shore drilling operations, constitute less than 6.9% of the discharge from the drilling process. And systems have been developed to meet and even exceed this requirement. For on-shore drilling operations, drilling fluid is typically diesel oil based and thus toxic to the environment, and a different set of disposal regulations applies.
Different regulations apply to land-based drilling operations because of the different environment from that of off-shore operations. For land-based operations, the residue of the drilling process is commonly gathered and transported to disposal sites. Disposal at such sites often involves placing the residue in underground repositories because the residue is itself toxic. The transportation of the waste is expensive and is meeting increasing resistence from the public. However, certain regulations such as those in Texas dictate that if drilling fluids remain on the cuttings at less than 1% by weight, then the cuttings do not have to be disposed of at a toxic waste site.
Thus, there remains a need for a way to dispose of the waste from land-based drilling operations that eliminates the need to transport and bury the waste. The present invention is directed to fulfilling this need in the art in which such volatile materials must be removed from granular solids by the reclamation of petroleum lubricated drilling fluids used in the exploration and production of petroleum oils. While drilling mud is essentially a diesel or synthetic material based fluid composition, the drilling mud is frequently compounded with a lubricant material such as diesel, crude oil, or other non-water petroleum based constituent to facilitate the mud""s lubricating characteristics. These lubricant materials present a biohazard, and the present invention is directed to minimizing or eliminated this biohazard on land-based drilling operations.
The present invention is directed to the treatment of cuttings from the drilling process to the point that the cuttings need not be disposed of as toxic waste, but can be disposed of directly at the drill site by land farming. Current cuttings dryers from Hutchison-Hayes International, the Assignee of the present innovation, reduce the oil content of drill cuttings to between 2% and 3%. This low level of oil content is still too high to disposed of the cuttings directly to the environment, but treatment of the cuttings either upstream or downstream of the cuttings dryer by a chemical additive reduces the oil content still further. The oil content of the cuttings can effectively be reduced to below 1% within the cuttings dryer itself, permitting the cuttings to be spread over the surrounding area around the drill site, much as fertilizer is spread on the land.
Although other additives may be used to good effective, presently preferred additive is Diethylene Glycol Monoethyl Ether (HOCH2CH2OCH2CH2OC2H5), sold under the tradename Carbitol. Whatever additive is used, it must have certain physical and chemical characteristics. The additives which find application in the present invention are primarily solvents, surfactants, demulsifiers, and dispersants, or blends of these products. Other additives may include enzymes, saponifiers, and certain biological agents including micro-organisms. The additive must react quickly with the drilling mud residue on the cuttings and break down the oil of the drilling mud to a non-toxic reaction product. Further, the additive itself must be non-toxic to permit the immediate disposal of the final stage cuttings directly to the soil. Further, if the additive is added to the fluids-laden cuttings upstream of the cuttings dryer, the additive must not adversely alter the makeup of the drilling fluid so that the fluids discharge from the cuttings dryer can be directed back to the drilling mud system for reuse.
Thus, the present invention comprises injecting an additive to cuttings containing a detectable amount of hydrocarbon-based drilling fluid and mixing the cuttings and additive to the point where the amount of hydrocarbon-based drilling fluid is less than 1% by weight. The present invention also includes the additional step of taking the mixture of cuttings and additive and disposing of the mixture directly to the soil, preferably in the immediate vicinity of the well site.
The additive may be mixed with the oil-bearing cuttings either upstream or downstream of the cuttings dryer. For effective mixing, the cuttings are preferably placed in a mixing component, such as for example an auger or the like, and exposed to a fine spray of the additive. The mixing component may thus be placed upstream of the cuttings dryer, and the additive/cuttings mixture then directed to the cuttings dryer. Alternatively, the mixing component is preferably placed downstream of the cuttings dryer where the oil content of the cuttings is substantially reduced from that of the upstream side of the cuttings dryer. However, the structure of the mixing component is the same or similar to that previously described.
The present invention further provides the feature of varying the rate of the additional of the chemical additive based on the rate at which cuttings are input into the system. The system senses the load, i.e. the cuttings loading, and alters the operation of the cuttings dryer accordingly, and simultaneously in a coordinated fashion increases or decreases the rate of additional of the treatment chemical.
These and other features and advantages of this invention will be readily apparent to those skilled in the art.